How do I stretch a strip to work with the speed control effect without loosing footage?
Click and Drag on the End part of the clip with the minimal arrow to manually stretch it out and extend.  Make sure there is empty room to extend.  Use the correct side of mouse to click.  My mouse is differently set.

The panel also allows you to type in length. Press n to display panel.

Middle Click moves the entire strip. Do not click in the Middle for this task.